Function Principle; Analog Inputs Ai1 And Ai2; Digital Outputs Do1 And Do2; Cpu - Siemens SIPART DR21 Manual

2 Technical Description

2.5 Function principle

2.5 Function principle
2.5.1

Standard controller

D General
The SIPART DR21 controller operates on the basis of a modern, highly-integrated microcon-
troller in C-MOS-technology. A large number of functions for controlling processing plants
are stored in the instrument's ROM. The user can adapt the controller to the task himself by
configuring it.
D Analog inputs AI1 and AI2.
The analog inputs of the SIPART DR21 are designed for 0/4 to 20 mA input signals. The in-
puts have an input load resistance of 248 Ω and are potential-bound. The start value 0 mA
or 4 mA is determined by the structure switches S4 and S5.
D Outputs for the manipulated variable Y
The standard controller has the following outputs
K-output: switchable between 0 or 4 to 20 mA, potential-bound (S56)
S-output: two relays, NOC, interlocked in factory setting, built-in spark quenching de-
signed for wiring with medium contactors. Other functions can be assigned
to the relay outputs by configuration (structure switches S57 to S68), e.g.
manipulated variable output ±Δy in S-controllers.
D Digital outputs DO1 and DO2
The digital outputs are short-circuit-proof and can drive commercially available relays or the
interface relays 6DR2804-8A/8B directly. Different functions can be assigned to the digital
outputs by configuration (structure switches S57 to S68).
D Digital inputs DI1 and DI2
The inputs are designed in 24-V-logic and are potential-bound. The function is assigned to
the input by configuration of the controller (structure switches S23 to S33).
D CPU
The microcontroller used has integrated AD- and DA-converters and watchdog-circuits for
cycle monitoring. The processor operates with a 64k EPROM (on a socket and therefore
replaceable) and a 1k RAM.
The SIPART DR21 program runs with a fixed cycle time of 100 ms. A process image is gen-
erated at the start of every routine. The analog- and digital inputs, the operation of the front
keyboard and the process variables received by the serial interface are acquired or
accepted. All calculations are made according to the stored functions with these input sig-
nals. Then output to the display elements, the analog outputs and the digital outputs and
26
Manual
SIPART DR21
C73000-B7476-C143-08